CMRT09

Stilla, Uwe

Bibliographic data

Monograph

Persistent identifier:: 856955019

Author:: Stilla, Uwe

Title:: CMRT09

Sub title:: object extraction for 3D city models, road databases, and traffic monitoring ; concepts, algorithms and evaluation ; Paris, France, September 3 - 4, 2009 ; [joint conference of ISPRS working groups III/4 and III/5]

Scope:: X, 234 Seiten

Year of publication:: 2009

Place of publication:: Lemmer

Publisher of the original:: GITC

Identifier (digital):: 856955019

Illustration:: Illustrationen, Diagramme, Karten

Language:: English

Usage licence:: Attribution 4.0 International (CC BY 4.0)

Publisher of the digital copy:: Technische Informationsbibliothek Hannover

Place of publication of the digital copy:: Hannover

Year of publication of the original:: 2016

Document type:: Monograph

Collection:: Earth sciences

Chapter

Title:: DENSE MATCHING IN HIGH RESOLUTION OBLIQUE AIRBORNE IMAGES M. Gerke

Document type:: Monograph

Structure type:: Chapter

In: Stilla U, Rottensteiner F, Paparoditis N (Eds) CMRT09. IAPRS, Vol. XXXVIII, Part 3/W4 — Paris, France, 3-4 September, 2009 DENSE MATCHING IN HIGH RESOLUTION OBLIQUE AIRBORNE IMAGES M. Gerke International Institute for Geo-Information Science and Earth Observation - ITC, Department of Earth Observation Science, Hengelosestraat 99, P.O. Box 6, 7500AA Enschede, The Netherlands, gerke@itc.nl KEY WORDS: Adjustment, Bundle, Calibration, Matching, Point Cloud, Rectification ABSTRACT: An increasing number of airborne image acquisition systems being equipped with multiple small- or medium size frame cameras are operational. The cameras normally cover different viewing directions. In contrast to vertical images, those oblique images have some specific properties, like a significantly varying image scale, and more occlusion through high raising objects, like buildings. However, the faces of buildings and other vertically extended objects are well visible and this is why oblique images are used for instance for visualization purposes. This paper shows results from applying the sophisticated Semi-Global-Matching technique to a set of oblique airborne images. The images were acquired by two systems, namely FLI-MAP 400 (Fugro Aerial Mapping B.V.) and Pictometry (BLOM Aerofilms) over the same area. After the joint adjustment of the images, dense matching and forward ray intersection was performed in several image combinations. The disparity maps were evaluated through the comparison with a reference map derived from LIDAR which was acquired in parallel with the FLI-MAP system. Moreover, the 3D point clouds were analyzed visually and also compared to the reference point cloud. Around 60 to 70 percent of all matches were within a range of ± 3pix to the reference. Since the images were acquired in different flight configurations, the impact of different intersection angles and baselines to the triangulation is quite obvious. In general, the overall structures on the building faces are well represented, but the noise reduction needs further attention. 1 INTRODUCTION An increasing number of airborne image acquisition systems are operational (Petrie and Walker, 2007). Because of the availability of low-cost digital cameras with small or medium sized sensors, some of those systems carry multiple cameras covering differ ent viewing directions. For instance from Pictometry 1 image are available already for a number of cities and they are accessible in the category ’’birds eye view” in Microsoft Bing Maps 1 2 (formerly known as Virtual Earth). The use of oblique images for topographic mapping purposes was shown in quite some papers. In (Hôhle, 2008) height determina tion from single oblique images is demonstrated. The verifica tion of vector data using oblique imagery is shown in (Mishra et al., 2008). Due to the fact that building façades are well vis ible in oblique images, some researchers concentrate on how to automatically extract façade textures (Früh et al., 2004, Wang et al., 2008). Besides, the oblique images are interesting for cadas tre applications, because the building outline as defined at the vertical wall is directly visible (Lemmen et al., 2007). Com pared to vertical airborne images, oblique images have some spe cific properties. Depending on the tilt angle, the scale within the imaged scene varies considerably. Moreover, vertical struc tures of raised objects like buildings or trees are imaged, but the (selfjocclusion by those objects is much more significant com pared to the vertical image case. Another interesting application and research domain concerns the derivation of high dense point information through image mat ching techniques. The benchmark results from the Middlebury 3 testsets show that high quality state-of-the-art techniques to dense matching are available. If it is possible to apply those techniques to oblique airborne images, interesting new applications would arise, or support existing ones, like the ones listed above. In gene 1 http://www.pictometry.com 2 http://www.bing.com/maps 3 http://vision.middlebury.edu/stereo/ (accessed 15 March 2009) ral, point clouds as derived from dense matching in oblique ima ges can be a complementary data source to airborne laser scan ning, as those devices normally do not capture dense points on vertical structures. Of course, the traditional use of this kind of data to produce digital surface or terrain models is another possi ble application. In (Besnerais et al., 2008) an approach to dense matching in obli que airborne images is presented. The authors develop a pixel wise similarity criterion which accounts for the special viewing geometry of oblique images. A dense depth map is obtained through global regularization. The approach was tested on a num ber of test images and showed good results. However, the ground sampling distance of the used images was not smaller than 1,4m, mostly it was even larger, up to 20m. This paper evaluates the application of the Semi-Global-Matching technique (SGM, see (Hirschmtiller, 2008)) to a set of high reso lution FLI-MAP 4 and Pictometry images. One particular façade of a building is normally only visible in images taken from one viewing direction, resulting in a relatively bad intersection angle in object space. Thus, the main objective of this paper is to eval uate the overall accuracy of the derived 3D point cloud as derived from a forward intersection of matched points. Although other - may be better performing- algorithms for dense matching exist (Seitz et al., 2006) we chose SGM, because it demonstrated al ready its fitness for the photogrammetric production process, c.f. (Hirschmüller et al., 2005). As no sufficient calibration and orientation information was avai lable, the whole block first needed to be adjusted. The method for bundle block adjustment, including self-calibration of multi ple devices and employing scene constraints to enhance the scene geometry was introduced and tested in (Gerke and Nyaruhuma, 2009). The dense matching algorithm then was applied to sev eral combinations of stereo images, and results were evaluated through LIDAR data which was acquired from the FLI-MAP sys tem. 4 http://www.flimap.nl

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